This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Mining shovels are often powered by hydraulic pressure systems. In these systems, hydraulic fluid is transmitted throughout the machine to various actuators, or hydraulic cylinders, where the fluid is converted into energy for powering the machine's components as necessary. For instance, a dipper assembly of the shovel may be powered by an actuator. In this case, an operator may provide a command to the actuator powering the dipper via a control system, causing the actuator (e.g., a piston rod of the actuator) to retract or extend in order to move the dipper assembly. As an example, the actuator may be used to apply a crowding force into a bank of material in order to fill the dipper with mining material.
In some instances, such as when filled with material, the dipper assembly may move without an operator command due to its own weight, inadvertently extending or retracting the cylinder. When this occurs, a chamber of the cylinder may expand, creating a void in the cylinder. When the dipper assembly is moved by operator command, a source of fluid may be manually or automatically provided to fill the void and prevent cavitation. However, during a static condition (i.e. when the dipper assembly moves without an operator command), fluid is not typically provided without an operator command to fill the void, often leading to a cavitation within the cylinder. Cavitation within a hydraulic system can cause unwanted noise, damage to the hydraulic components, vibrations, a loss of efficiency, and can reduce the useful life of the system and its components.
Mining shovels may include a hydraulic system having a valve for controlling the flow of hydraulic fluid from a pump to a hydraulic cylinder. An example of such a hydraulic system can be found in U.S. Pat. No. 5,960,695 issued Oct. 5, 1999, for “System and Method for Controlling an Independent Metering Valve,” which discloses an independent metering valve that includes four independently operable, electronically controlled metering valves to control fluid flow between a pump and hydraulic cylinder. The disclosed independent metering valve is not controlled to automatically respond to void conditions within the associated hydraulic cylinder, however, and the cylinder may be susceptible to voiding and/or cavitation when the cylinder is not being controlled via an operator command.